This is book 21 of the "Stephanie Plum" series.

This note does not contain major spoilers for the book.

Rangeman security is shut down by a polonium release—an assassination attempt. And apparently a dry-run for something even worse. The FBI is involved and not sharing information.

Ranger thinks the assassin is somebody he interacted with years back in Afghanistan, who has a grudge. He's also a professional torturer specializing in disembowlment.

The cast of characters remains wild and wacky and not very believable, and not long on people I really care about. Stephanie isn't hopeless, though. She's too nice to everybody, but that's an acceptable character flaw that leads to plot advancement.